Hypergolic bipropellant propulsion process using boron components

ABSTRACT

1. THE METHOD OF DEVELOPING A THRUST WHICH COMPRISES REACTING A BORANE COMPONENT SELECTED FORM THE GROUP CONSISTING OF BORON HYDRIDES, HYDROCARBON SUBSTITUTED BORON HYDRIDES, AND MIXTURES THEREOF, AND A HYDRAZINE COMPONENT SELECTED FROM THE GROUP CONSISTING OF HYDRAZINE, HYDROCARBON SUBSTITUTED HYDRAZINES, AND MIXTURES THEREOF, IN A CHAMBER WHICH IS CLOSED EXCEPT FOR A CONSTRICTED EXHAUST NOZZLE, AND EXPELLING THE RESULTANT REACTION PRODUCTS THROUGH SAID NOZZLE TO PRODUCE A REACTION THRUST ON SAID CHAMBER.

United States Patent @fiee 3,613,371 Patented Oct. 19, 1971 3,613,371HYPERGOLIC BIPROPELLANT PROPULSION PROCESS USING BORON COMPONENTSLawrence J. Edwards, Zelienople, Pa, assignor to Callery ChemicalCompany, Pittsburgh, Pa. N Drawing. Filed Feb. 4, 1959, Ser. No. 791,231Int. Cl. C06d 00, 5/06 U.S. Cl. 60214 9 Claims This invention relates toreaction engines and more particularly to new bipropellants useful inconnection with rockets or rocket engines.

The rockets or rocket engine is a self-contained reaction engine in thatit does not require the use of air to effect an energy-producingchemical reaction. Bipropellants consist of two separated componentswhich are mixed together at the time of use in a combustion chamberwhere they are reacted to produce a jet thrust as the products of thereaction exhaust through a nozzle at the end of the combustion chamber.These bi-component propellants are commonly called bipropellants. Priorbipropellants have used fuel and oxidizer components. The fuelsheretofore generally used or considered for use include alcohols,hydrocarbons such as JP-4, aniline, nitrogen hydrides such as hydrazine,and boron hydrides and their derivatives such as diborane andpentaborane. The oxidizers generally used include nitric acid andnitrogen oxides, hydrogen peroxide, and liquid oxygen. Liquid fluorinehas also been considered for use as an oxidizer. Energy is produced fromthe combustion or oxidation of the fuel by the oxidizer.

The thrust-producing capacity or performance rating of a particularpropellant system is commonly referred to as the specific impulse, whichis usually expressed as pounds of thrust available per pound ofpropellant per second. The reported specific impulses for propellantscurrently in use range from about 150 to 280 lb. sec./lb. Those factorsinherent in the propulsion reaction that significantly effect thespecific impulse are the reaction temperature and the molecular weightof the reactant products. Specific impulse is directly proportional tothe square root of the reaction temperature and inversely proportionalto the square root of the molecular weight of the reaction products.Another major factor governing specific impulse is the ratio of chamberpressure to exit pressure; however, this is adjusted by variations inthe configuration of the exhaust nozzle and may be adjusted independntlyof propellant properties.

There are certain limitations of the performance of conventionalfuel-oxidizer bipropellants which are inherent in the nature of theenergy-producing reactions. The molecular weight of the reactionproducts is relatively high since the production of energy depends onthe combination of comparatively heavy elements of the oxidizer withelements of the fuel, e.g. the combination of hydrogen and oxygen toproduce H O or the production of oxides of carbon. Also, the oxidationproducts tend to dissociate at the high combustion temperature involvedand a substantial amount of the potential available energy is lost bythis dissociation, e.g. the dissociation of CO to C0. Although thespecific impulse is increased with an increase in combustiontemperature, the construction of combustion chambers for very hightemperature propellants is expensive or impracticable because of thelack of suitable materials of construction. It is, therefore, especiallydesirable to have available propellants that develop a high specificimpulse at moderate temperatures.

It is an object of this invention to provide new bipropellants for usein rockets or rocket engines that produce a high specific impulse.Another object is to provide a bipropellant that produces a highspecific impulse at a moderate reaction temperature. A further object isto provide a bipropellant system that does not require a conventionaloxidizer component.

Using the borane-hydrazine propellants of this invention, theenergy-producing reaction is a highly exothermic reaction between aboron hydride or hydrocarbon derivative of a boron hydride and hydrazineor a hydrocarbon derivative of hydrazine. For example, the reactionbetween pentaborane(9) and hydrazine proceeds accordlng to with arelease of 4250 B.t.u. per pound of bipropellant.

The borane-hydrazine bipropellant reaction is a high energy reaction incomparison with conventional fueloxidizer bipropellants; for example,the hydrazine-oxygen reaction releases 3600 B.t.u./lb. Further, the newbipropellants produce large volumes of hydrogen (with a molecular weightof 2), in contrast to the consumption or reaction of hydrogen inconventional fuel-oxidizer bipropellants. For this reason the effectivemolecular weight of the reaction products is lower than that obtainablefrom conventional bipropellants.

The reaction temperature of the new borane-hydrazine bipropellants iscomparable to combustion temperature of those conventional bipropellantswhich can develop only a moderately high specific impulse. For example,the reaction temperature of the pentaborane(9)-hydrazine bipropellant isabout 4600 R, which is approximately the same as the combustiontemperature of ethyl alcoholhydrogen peroxide bipropellant. Because ofthe low effec tive molecular weight of the reaction products, a highspecific impulse is obtained at the desirable moderate temperature.Further, since the reaction products do not dis sociate to anysignificant amount there isv little loss of the potential availablechemical energy. For example, the specific impulse of thepentaborane(9)-hydrazine bipropellant at a combustion chamber pressureof 1000 p.s.i.a. and an exit pressure of 1 atmosphere is about 338 lb.sec./ 1b., and at a chamber pressure of 300 p.s.i.a. and exit pressureof 1 atmosphere the specific impulse is about 297. In comparison, thehydrazine-oxygen bipropellant has a calculated specific impulse of 263lb. sec./lb. at a chamber pressure of 300 p.s.i.a.

Specific impulses for some proposed fuel-oxidizer propellants havepreviously been calculated which approach the specific impulseobtainable from the hydrazine-borane bipropellants; however, the highspecific impulse depends primarily on an extremely high combustiontemperature. For example, the hydrazine-fluorine propellant has acalculated specific impulse of 316 at a chamber pressure of 500p.s.i.a., but the combustion temperature is 7940" F. It is apparent thatsuch high temperature creates a difficult problem of engineering designand materials of construction of the combustion chamber which areavoided with the moderate reaction temperature of the new borane'-hydrazine bipropellants.

The stable liquid boron hydrides, such as pentaborane(9) andhexaborane(l0), are preferred borane components of the propellantbecause they are easily handled, stored, and pumped. Other boronhydrides, such as diborane, tetraborane, and decaborane, may be used aspropellant components in generally the same manner although moresophisticated storage or metering systems may be required. For example,decaborane (M.P. 99.7 C.) is a solid at ambient conditions and it may beinjected as a slurry in another borane or in solution in a hydrocarbon;preferably it is melted and injected as any other liquid fuel.

Hydrocarbon substituted boron hydride may be as well as theunsubstituted boron hydrides. Suitable materials include loweralkyldiboranes such as mono-, di-, tri-, and tetra-, methyldiboranes,and ethyldiboranes; alkyl substituted higher boron hydride such asalkyltetraboranes, alkylpentaboranes, alkyl hexaboranes, andalkyldecaboranes such as methyl substituted decaboranes;borohydrocarbons such as the reaction product obtained from reaction ofacetylene and boranes; other similar borohydrocarbons; and mixturesthereof. Hydrocarbon substituted higher boron hydrides are made, forexample, by reacting a halogenated hydrocarbon with the boron hydride inthe presence of an aluminum halide, as disclosed in the copending,coassigned application of Wunz and Stang, Ser. No. 756,058, filed Aug.14, 1958. Although the specific impulse obtained from the hydrocarbonsubstituted boron hydrides is somewhat less than that obtained fromunsubstituted boron hydrides, they may be preferable for certainapplications because of their stability, resistance to hydrolysis, lowvapor pressure, and lower toxicity.

Hydrazine, N H is the preferred hydrazine component of the propellantsince its use results in the highest specific impulse with any boranecomponent, but hydrocarbon substituted hydrazine may be used if desired,e.g. lower alkyl hydrazines such as methyl hydrazine, sym-dimethylhydrazine, unsym-dimethylhydrazine, trimethyhydrazine, ethylhydrazine,diethylhydrazines, and triethylhydrazine.

When hydrocaron substituted propellant components are used, the reactionproducts include boron nitride, boron carbide, carbon, hydrogen, andsmall amounts of dissociation products such as boron and nitrogen.

The borane-hydrazine bipropellants of the invention may be used in thesame manner and in the same type of engine as is used with conventionalfuel-oxidizer bipropellants. The hydrazine component and the boranecomponent are contained in separate tanks from which they are fed to thecombustion chamber. In order to ob tain the best utilization of theavailable stored chemical energy they are preferrably fed instoichiometric proportions. The bipropellants are pumped into thechamber; however, they may be injected by pressurizing the tanks with aninert gas. Impingement injectors, spray injectors, non-impinginginjectors, and other types of injectors may be used. The unsubstitutedhydrazine-unsubstituted boron hydride propellants are hypergolic at roomtemperature and atmospheric pressure so auxiliary ignition or preheatingof the combustion chamber is not normally required. If the combustionchamber is at very low temperature, it may be preheated before beginninginjection of the propellant to prevent an accumulation of unreactedpropellant which may then spontaneously ignite and cause an explosion inthe chamber. The hydrocarbon substituted propellant components do notreliably ignite spontaneously at ambient conditions, so ignition byspark plug, hot wire, or other conventional methods should be used.Ignition may be conveniently accomplished by introducing small amountsof oxygen, hydrogen peroxide, or other oxidizer into the combustionchamber. The reactions, however, are self-sustaining at the hightemperature of the combustion chamber under operating conditions, soonly an initial ignition is required.

According to the provisions of the patent statutes, I have explained theprinciple and mode of practicing my invention and have described what Inow consider to be its best embodiments. However, I desire to have itunderstood that, within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described.

I claim:

1. The method of developing a thrust which comprises reacting a boranecomponent selected from the group consisting of boron hydrides,hydrocarbon substituted boron hydrides, and mixtures thereof, and ahydrazine component selected from the group consisting of hydrazine,hydrocarbon substituted hydrazines, and mixtures thereof, in a chamberwhich is closed except for a constricted exhaust nozzle, and expellingthe resultant reaction products through said nozzle to produce areaction thrust on said chamber.

2. A method according to claim 1 in which the hydrazine component ishydrazine.

3. A method according to claim 1 in which the borane component is aboron hydride.

4. A method according to claim 2 in which the borane component isdiborane.

5. A method according to claim 2 in which the borane component ispentaborane(9).

6. A method according to claim 2 in which the borane component isdecaborane.

7. A method according to claim 2 in which the borane component is alower alkyl substituted higher boron hydride.

8. A method according to claim 7 in which the borane component is amethyl substituted decaborane.

9. A method of operating a jet propelled device which comprisesseparately supplying to the reaction chamber of the device hydrazine anddecaborane to produce thrust.

References Cited Clark, Ordnance, vol. 36, pp. 661-3 (1952), Penner, J.Chem. Ed., pp. 379 (January 1952).

BENJAMIN R. PADGETT, Primary Examiner U.S. Cl. X.R.

1. THE METHOD OF DEVELOPING A THRUST WHICH COMPRISES REACTING A BORANE COMPONENT SELECTED FORM THE GROUP CONSISTING OF BORON HYDRIDES, HYDROCARBON SUBSTITUTED BORON HYDRIDES, AND MIXTURES THEREOF, AND A HYDRAZINE COMPONENT SELECTED FROM THE GROUP CONSISTING OF HYDRAZINE, HYDROCARBON SUBSTITUTED HYDRAZINES, AND MIXTURES THEREOF, IN A CHAMBER WHICH IS CLOSED EXCEPT FOR A CONSTRICTED EXHAUST NOZZLE, AND EXPELLING THE RESULTANT REACTION PRODUCTS THROUGH SAID NOZZLE TO PRODUCE A REACTION THRUST ON SAID CHAMBER. 